A multi-sensor framework in google earth engine for spatio-temporal trend analysis of water quality parameters in Anzali lagoon

Abstract

Abstract The Anzali wetland is one of the internationally known freshwater wetlands which provides habitats for many plants and migratory birds, and plays the role of a treatment plant for running water into the Caspian Sea. However, its lagoon is getting shallower due to the inflow of sediment and deposition of organic detritus, and its water quality is deteriorating due to the inflow of wastewater and solid waste from neighboring cities. Therefore, monitoring of water quality parameters (WQP) in Anzali Lagoon is deemed a priority for protection and prevention of its degradation. The current study investigates the environmental condition of the wetland between 2014 to 2021 using remote sensing technology. A multi-sensor framework was developed in google earth engine for spatio-temporal trend analysis of water quality parameters in Anzali lagoon. Water quality parameters incluing TSS, TDS, pH and nitrate were derived using Landsat satellite data based on the calibrated regression equations introduced for this wetland. Spatio-temporal variations of WQP was depicted to determine the critical points and evaluate the trend analysis. The results showed that the WQP fluctuate significantly over time. The spatial distributions indicated that the critical points of the lagoon are changing from the Western to the center and Eastern parts. The comparison of the WQP parameters with the environmental standards confirmed that the lagoon condition is in critical stage, especially in terms of TSS. Nitrate values showed that 50% of the lagoon area exceeds the environmental standards, which indicates the nutritional status. The investigated WQP has had a significant positive trend in most areas, so the lagoon is under high environmental risk and unfriendly human activities should be controlled.